The present invention relates generally to operations performed in a subterranean well and, in an embodiment described herein, more particularly provides a system for remotely controlling operation of tools positioned within the well.
A large variety of tools have been designed to operate within subterranean wells. Of these, many are operated by application of fluid pressure, or differential fluid pressure, thereto. For example, tester valves, retainer valves, subsea test trees, pressure actuated sliding sleeve valves, etc. all depend for their operation, at least in part, on fluid pressure being applied selectively thereto in order to accomplish an objective, such as opening or closing a flow passage.
In some circumstances, fluid pressure may be applied directly to a pressure actuated tool in a well. For example, some circulating valves may be opened by merely applying fluid pressure at the earth's surface to a tubing string in which the circulating valve is interconnected. In that case, the tubing string directly transmits the fluid pressure from the earth's surface to the circulating valve.
However, in other circumstances, it is not practical for downhole tools to be operated by application of fluid pressure to a tubing string. One of these circumstances is where multiple tools having multiple modes of operation are utilized. For example, in a subsea well testing operation, it is common to interconnect both a retainer valve and a subsea test tree in the tubing string. Each of the retainer valve and the test tree typically requires a control line and a balance line connected thereto, and the test tree typically requires a latch line connected thereto. Additionally, an injection line may be interconnected to the test tree in order to permit injection of fluid, such as chemical treatment fluid, into the tubing string.
Heretofore, the control lines, balance lines, latch line and injection line have been bundled and attached externally to the tubing string extending to the earth's surface. Unfortunately, however, this situation creates a number of problems. Installation of the lines and associated equipment is difficult and time-consuming and, therefore, expensive. The bundle of lines is susceptible to damage both during and after installation. Additionally, the lines themselves are very expensive and usually not reusable.
These problems, and others, are present in varying degrees in other operations involving downhole tools which are pressure actuated. In general, where it is has not been feasible or desirable to utilize the tubing string or the annulus between the tubing string and the wellbore to transmit fluid pressure from the earth's surface for operation of these tools, the fluid pressure has been transmitted through lines extending from the earth's surface to the tools.
From the foregoing, it can be seen that it would be quite desirable to provide a system for operating a pressure actuated downhole tool which eliminates or minimizes the number of lines extending to the earth's surface, which is convenient in installation and operation, which is economical and which minimizes damage to lines in its installation. Additionally, it would be desirable for the system to permit communication between the earth's surface and a downhole portion of the system, so that the system may be remotely controlled from the earth's surface and/or the downhole portion of the system may transmit data to the earth's surface. It is accordingly an object of the present invention to provide such a system and associated methods of controlling downhole tools.